Vue.createApp({
    data(){
    return {
    date:'00:00:00'
    }
    },
    mounted(){ //mounted()生命周期：DOM挂载后
    setInterval(()=>{
    let d = new Date();
    this.date = d.getHours()+':'+d.getMinutes()+':'+d.getSeconds();
    },1000);
    }
    }).mount("#app")